Accumulator



Feb. 27, 1951 R. s. MILLER 2,543,585

- ACCUMULATOR Filed Jan. 13, 1945 2 Sheets'-Sheet I INVENTOR. R. S. M lLLER ATTORNEY R. S. MILLER Feb. 27, 1951 ACCUMULATOR 2 Sheets-Sheet 2Filed Jan. 13, 1945 INVENTOR. R. S. MILLER ATTORNEY Patented Feb. 27,1951 ACCUMULATOR Raymond S. Miller, Los Angcles, Calm, assignor toBendix Aviation Corporation, South Bend, Ind, a corporation of DelawareApplication January 13, 1945, Serial No. 572.623

5 Claims.

' This invention relates to accumulators for use in hydraulic systemsand relates particularly to a bladder construction for use in suchaccumulators to separate the working fluid, usually a liquid, from agas, usually air, which is compressed to maintain a pressure on theworking fluid.

An object of the invention is to provide a bladder construction that issimple and practicable and is effective to reduce or prevent thetrapping of working fluid.

Other more specific objects and features of the invention will becomeapparent from the description to follow of a particular embodiment thatis illustrated in the drawing.

Accumulators of the general type to which this invention relates are incommon. use in hydraulic systems for storing hydraulic fluid underpressure and supplying it to the system without excessive loss ofpressure when the supply pump is not operating or when the demandexceeds the capacity of the pump.

A common type of such accumulator consists of a generally sphericalsteel shell having an air opening at one end and a liquid opening at theother end. To prevent mixing of the liquid with the air the shellcontains a generally spherical flexible bladder having an openingsecured to the shell at the air opening thereon so that the space withinthe bladder is filled with air and any space between the bladder andshell is filled with the working liquid. Normally, the bladder is abouthalf collapsed so that the space between the bladder and shell filledwith working liquid is equal to about half the total volume of theshell. l

The air is, of course. compressed to the pressure of the liquid, and ifthe pressure of the liquid in the system (which is connected to theliquid opening of the shell) diminishealiquid is forced out of the shellby the pressure of the air within the bladder. The bladders are intendedto be so designed that the closed end telescopes into the portionadjacent the air opening when liquid flows into the shell and isdistended when liquid is withdrawn from th shell. If this telescopingaction takes place uniformly in the manner intended, very nearly all ofthe liquid is forced out of the shell when th pressure in the system isreduced sufficiently to expand the bladder to the end of the shell wherethe liquid opening is located, resulting in substantially 100 per centvolumetric efliciency.

However, these bladders do not always expand and contract uniformly inthe desired and intended manner. For various reasons, some of which areknown and some are unknown, the bladders sometimes fold in unexpectedmanner when liquid is withdrawn from the shell, with the result that theend of the bladder adjacent the liquid opening may contact the shellaround the opening and efiect a seal therewith while another portion ofthe bladder more remote from the liquid opening is spaced from theshell. This results in the trapping of liquid by the bladder andprevents the escape of the liquid through the opening so that thevolumetric efficiency of the accumulator is reduced.

The present invention resides in the provision of external buttons orbosses on the bladder which bosses contact the shell and maintain thesurface of the bladder intermediate the bosses spaced away from theshell so that passages are provided for the flow of liquid toward theshell opening even though the portion of the bladder adjacent theopening be expanded against the shell before portions more remote fromthe opening contact the shell. This permits trapped liquid to escape andinsures a relatively high volumetric efliciency.

It has also been a common practice for some time to provide a metal discon the bladder juxtaposed to the liquid opening in the shell to coverthe opening when the bladder is full expanded and prevent the extrusionof the flexible bladder material into the opening. Such discs sometimesfit sufficiently close against the shell over their entire circumferenceto prevent or greatly hinder the escape of liquid if the bladder expandsin such a way as to carry the disc against the opening before all theliquid has been exhausted. In accordance with the present invention,trapping of liquid from this cause is prevented by providing raisedshoulders at intervals around the edge of the disc to prevent it fromsealing against the-shell, while at the same time, avoiding theprovision of gaps or cracks of sufficient width to permit extrusion ofthe bladder material.

The disc construction is preferably used in combination with the bossesor buttons on the exterior surface of the bladder, the two combining toprevent the trapping of liquid in most cases.

A full understanding of the invention may be had from the followingdetailed description with reference to the drawing in which;

Fig. l is a longitudinal section through an accumulator incorporating abladder in accordance with the invention;

Fig. 2 is a view looking at the closed end of 5 the bladder;

Fig. 3 is a sectional view taken in the equatorial plane of theaccumulator showing one shape that the bladder may assume when partiallycollapsed, the bladder being shown in plan.

Fig. 4 is a section taken in plane IV-IV-of Fig. 3;

Fig. is a section similar to Fig. 4 but showing the bladder expanded toa greater extent than in Fig. 4; and

Fig. 6 is a section similar to 4 and 5 showing the bladder almostcompletely expanded.

Referring first to Fig. 1 the accumulator therein disclosed comprises asubstantially spherical shell III having a liquid opening H at one endand having a relatively large opening l2 at the other end. In Fig. 1 theaccumulator is shown positioned with the liquid opening ii at the topand the large opening [2 at the bottom. which position is preferred bysome users because any air that might be mixed with the liquid enteringwith the opening Ii will rise to the top and will be ejected from theshell when liquid flows out. However, these accumulators are sometimesinstalled in other positions and when mounted on movable craft such asairplanes, they may be required to operate in any position.

The larg: opening I2 is normally closed by a plug [3 which is secured inplace by a lock ring or nut l4 that is screwed into the threaded outerportion of opening l2. The plug l3 in turndefines an air passage I5which is normally closed by a fitting [6 which permits the forcing ofair into the accumulator under pressure.

There is positioned within the shell I a bladder I! which bladder islocked to the shell by the plug I3 and communicates with the air passage15. The bladder II has a flange l8 at its opening l9 which flange isclamped between an annular shoulder 20 on the shell and an annularflange 2| on the plug l3. This effects a seal between the bladder andthe shell so that no air can escape from the inside of the bladder tothe space between the bladder and the shell.

The bladder I! is preferably provided with a stationary portion 22 whichis formed to fit snugly against that portion of the shell extending fromthe opening l2 substantially to the equator, and a flexible portion 23which extends from the equator to the closed end of the bladder and isadapted to fold into the stationary portion 22 to a lesser or greaterextent when liquid enters the shell opening II and compresses the airwithin the bladder. If air becomes completely exhausted from within thebladder, for any reason, and pressure liquid enters the opening ii theflexible portion 23 will be completely telescoped into the stationaryportion 22 and will be folded around an equatorial bead 24. This bead isprovided for two purposes. It reinforces the stationary portion 22 ofthe bag at the equator to help maintain that portion in contact with theshell Ill at all times. The head also provides a smooth shoulder aboutwhich the flexible portion 23 of the bladder can bend with a substantialradius of curvature to reduce the danger of the material cracking at thefold. v

The closed end of the bladder is reinforced with a pair of discs 25 and26 which are clamped together by a screw 21, the bladder having a smallorifice at its end to permit passage of the screw. These discs 25 and 26are provided to prevent the extrusion of the flexible bladder wall intothe liquid opening I l in case of failure of liquid pressure and intothe air passage IS in the event of failure of the air pressure. Theflexible portion 23 of the bladder preferably has a relatively fiat endspaced appreciably from the end of the shell when the bladder is in itsnormal, or unstressed, position. It is found that this constructiontends to promote the orderly collapse of the bladder when the liquidpressure is increased, and the orderly distension of the bladder againstthe wall of the shell progressively from the equator to the opening IIwhen liquid is being drawn from the accumulator.

As so far described. the bladder corresponds to those previously known,in which the general shape of the bladder was relied upon to preventundesired trapping of liquid in pockets formed between the bladder andshell. However, as a result of variations from the desired thickness ofthe bladder wall due to faulty manufacture, and as a result of reasonswhich areat present not fully known, bladders of the type describedsometimes expand irregularly and in such a manner that the bladder maybe forced against the wall of the shell over an area completelysurrounding the liquid opening ll while a portion of the bladder moreremote from the opening is still inwardly displacedfrom the'shell. Whenthis happened with the prior known constructions, the pocket trappingthe liquid was effectively cut ofi from the liquid opening H so that thevolumetric efficiency was reduced.

The present invention resides in the provision of small buttons orbosses 28 on the exterior surface of the flexible portion 23 of thebladder and the provision of' a plurality of raised bosses or shoulders30 on the outer surface of the outer disc 25. The bosses 28 on thebladder contact the shell first and maintain the outer surface of thebladder intermediate the bosses in spaced relation with respect to theshell, so that fluid trapped between the bladder and the shell at apoint spaced away from the opening II can still flow between the bosses28 to the opening I I. The shoulders 30 on the outer disc 25 contact theshell when the bladder is fully expanded, leaving the portions 3! of theouter surface of the disc in spaced relation to the shell so thatliquid/loan escape therethrough to the liquid opening Ii.

The bosses 2B are preferably arranged in rows extending along meridiansof the bladder as shown in Fig. 2. In that figure, the bosses 28 arearranged in short rows lb! and in longer rows 28!. The pattern can bevaried, but it seems to be unnecessary to make all the rows of fulllength. Trapping most often results from sealing of the bladder againstthe shell over an area closely surrounding the opening II and it is,therefore. desirable to have the bosses spaced quite close together overthis area. However, when the trapping occurs at points adjacent theequator, the liquid is exhausted from the trapping area by the bosses 28in the long rows Zlil, even tnough the rows are spaced relatively farapart.

It is found that the shoulders 30 on the outer disc 25 can rise about.025" above the general outer surface of the disc 25 without making gapswide enough to damage the bladder wall when full air pressure is appliedwithin the bladder and the liquid opening Ii is opened to theatmosphere. At the same time, the gaps provided by shoulders .025" highpermit sufllciently free flow of liquid therethrough. The dimensions ofthe buttons or bosses 28 are not particularly critical. They may beapproximately A" in diameter and approximately 1 high and are preferablyformed integrally with the bladder wall by the use of a suitable mold.In general, the height of the bosses is of the same order of magnitudeas the thickness of the bladder wall although it is usually somewhatless.

Various patterns of distribution of the bosses may be used. Theparticular pattern shown in Fig. 2 has been found suitable for abladder, the long rows 28! being spaced 30 apart with one short row 282containing two buttons positioned between each adjacent pair of longrows.

On the other hand, ona bladder for a l accumulator, the long rows may bespaced 60 apart, with three short rows of two buttons each spacedbetween each adjacent pair of long rows.

In a bladder for a 5" accumulator the long rows 28l may also be spaced60 apart but with only three bosses in each long row, and with threeshort rows 282 of only one button each positioned between each adjacentpair of long rows. In a bladder for a 10" accumulator the outermostbosses may be spaced radially 3%" from the axis of the bladder. In the7%" size the outermost bosses may be spaced 3%" from the bladder axis,and in the 5" bladder the radial spacing from the axis of the outermostbuttons may be approximately 2' The views of Figs. 3 to 6 illustrate howfluid can be trapped in an accumulator having a. biadderwithout thebosses 28, and how the bosses prevent the trapping.

Referring first to Fig. 3, the flexible end of the bladder is shown in ashape which it may assume as it is being expanded, in response towithdrawal of liquid through the opening II. It will be observed thatthe bladder has not folded along a circular line but instead has foldedin the general shape of a triangle. It is found in practice that thebladders usually fold along an irregular line although not always inthree lobes as shown in Fig. 3. Sometimes it may fold in four or fivelobes instead of three. The irregular folding probably results chieflyfrom the fact that the thickness of the bladder wall produces unequaltension and compression in the inner and outer surfaces, but regard essof the exact cause it seems impossible in practice to construct bladdersthat will telescope in a perfectly symmetrical manner.

As best shown in the section of Fig. 4, the lobular folding of thebladder causes it to approach the shell closely at a point 50 on oneside of the liquid opening ll. while being bu'ged away from the shell ata point 5| on the other side of the liquid opening. As liquid continuesto flow out of the liquid opening H, the bladder may contact the shellall around the liquid opening H, as shown in Fig. 5, while the portion5| is still bulged inward.y away from the shell. This results in theformation of a pocket 52 which would be cut off completely from theliquid opening I] if the bosses 28 were not present. However, the bosses28 prevent a sealing contact between the bladder and the shell in a zonesurrounding the opening H, and the liquid therefore has a path of escapeout of the pocket. Assuming that the pressure in the liquid openingremains less than the pressure of the air within the bladder, theportion 5| of the bladder will be forced out until all the bosses 28 arein contact with the shell as shown in Fig. 6. By the time all the bosseshave contacted the shell very little liquid will be left in the spacessurrounding the bosses. If the liquid drain continues, resulting in asubstantial reduction of the pressure in the liquid opening below theair pressure within the bladder, the bladder wall will be distorted toforce substantially the entire outer surface of the iseases bladderagainst the shell except for a very narrow space surrounding each boss,and the liquid that is left trapped in these small spaces is relativelysmall and unimportant.

Although for the purpose of explaining the invention a specificconstruction has been described in detail, various changes from theexact construction shown can be made without departing from theinvention which is to be limited only to the extent set forth in theappended claims.

I claim:

1. An accumulator bladder for use in an accumulator shell having twospaced fluid openings, said bladder being of flexible material adaptedto be secured to the shell adjacent one of the openings and incommunication therewith, whereby it constitutes a fluid-tight movablepartition within the shell between said two openings, in which at leasta portion of the exterior surface of said bladder is provided with aplurality of spaced bosses for initially contacting the shell upondistension of the bladder and providing paths for escape to the other ofsaid openings in the shell of ,fluid trapped between the bladder and theshell, said .bosses being spaced from each other in all directionswhereby they provide paths for escape of trapped fluid in a plurality ofdirections from a trappin area.

2. A bladder as described in claim 1 in which said bosses are located onthat portion of the bladder surrounding the said other opening when thebladder is distended against the shell.

3. A bladder for use in an accumulator shell having two spaced fluidopenings, said bladder being of flexible material and adapted to besecured to the shell adjacent one of said openings and communicatingtherewith whereby it constitutes a fluid-tight'movable partition withinsaid shell between said two openings, and a rigid reinforcement securedto said bladder at the point therein juxtaposed to the other of saidopenings v in said shell, said reinforcement having an irregular contouralong its edge whereby it contacts the shell only at spaced intervals toprovide narrow gaps between the reinforcement and the shell-for escapeof fluid into said other opening when pressed thereagainst, whilepreventing extrusion of bladder material into said opening.

'4. An accumulator bladder for use in a generally spherical accumulatorshell having two diametrically opposite fluid openings, said bladderbeing of flexible material and adapted to be secured to the shelladjacent one of said openings and in communication therewith, a firstportion of said bladder adjacent said one opening being formed to fitagainst the shell and the remaining portion being flexible and adaptedto telescope into the first portion when the bladder is collapsed, thetelescoping portion of the bladder having a plurality of bosses on itsouter surface adapted to surround said other opening for providingpassages for the escape to said other opening of fluid trapped betweensaid bladder and said shell by movement of the bladder against saidother opening, said bosses being spaced from each other in alldirections whereby they provide paths fOr escape of trapped fluid in aplurality of directions from a trapping area.

5. A bladder for use in an accumulator shell having two spaced fluidopenings, said bladder being of flexible material and adapted to besecured to the shell adjacent one of said openings and communicatingtherewith whereby it constitutes a fluid-tight movable partition withinsaid shell between said two openings, and a rigid reinforcement securedto said bladder at the point therein juxtaposed to the other of saidopenings in said shell, said reinforcement being configured to definepassages for escape of fluid into said other opening when pressedthereagainst. while preventing extrusion of bladder material into saidopening, and the portion of the exterior surface of said bladdersurrounding said reinforcement having a plurality of spaced bossesthereon for initially contacting the shell upon distension oi thebladder and providing paths for escape to the said other opening offluid trapped between the bladder and the shell.

RAYMOND 8. m3;

8 REFERENCES crran The following references are of record in the tile 01this patent:

UNITED STATES m'nmrs Number Name Date 2,051,019 Arutunoi't Aug. 18, 19362,283,439 Herman May 19, 1942 2,349,321 White May 23, 1944 2,378,517Trautinan June 19, 1945 2,389,791 Lippincott Nov. 27,1945 2,389,792Lippincott Nov. 27, 1945.

